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    <title>Document</title>
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<script>
    /**
     * 自定义函数分类
     * 1、普通函数定义，function 函数名（参数）{函数体}
     * 2、把函数赋值给变量，通过变量调用函数
     * 3、匿名函数
    */

    function sayHello(userName){
        alert("hello " + userName);
    }
    sayHello("zhangsan");

    //匿名函数
    //没有返回值，返回undefined
    var showAge = function(age){
        var str = "年龄为：" + age;
    }
    console.log(showAge(20));

</script>
</html>